It is known to contact hydrocarbon oil with cracking catalyst particles by passing said hydrocarbon oil as an outer annular stream in a generally linear direction, imparting a centrifugal energy component to said stream and passing an inner gas stream concentrically with said outer stream through a restricted opening to bring said stream into contact with catalyst particles.
It would be advantageous, however, to reduce the relatively large pressure drop resulting from (i) the conversion of linear velocity of the hydrocarbon oil stream into a tangential velocity component corresponding to the afore-mentioned centrifugal energy component and (ii) the subsequent passage of said stream together with an at least partly unbroken inner gas stream through a restricted opening.
It has now been found that optimal mixing of a fluid with particulate solids can be attained with a relatively small pressure drop without requiring a separate inner fluid stream by introducing an annular fluid stream (preferably as a central, symmetrical, hollow-cone jet) directly into a solids stream.